File: templates/debug/source_code.html.twig

<div class="section source-code">
    <p>
        {{ 'help.show_code'|trans|raw }}
    </p>

    <button type="button" class="btn btn-default btn-lg btn-block" data-toggle="modal" data-target="#sourceCodeModal">
      <i class="fa fa-cogs" aria-hidden="true"></i> {{ 'action.show_code'|trans }}
    </button>

    <div class="modal fade" id="sourceCodeModal" tabindex="-1">
        <div class="modal-dialog modal-lg">
            <div class="modal-content">
                <div class="modal-header">
                    <button type="button" class="close" data-dismiss="modal" aria-label="Close">
                        <span aria-hidden="true">&times;</span>
                    </button>
                    <h4 class="modal-title"><i class="fa fa-code" aria-hidden="true"></i> {{ 'title.source_code'|trans }}</h4>
                </div>

                <div class="modal-body">
                    {% if controller %}
                        <h3><a href="https://symfony.com/doc/current/controller.html" target="_blank">{{ 'title.controller_code'|trans }}</a><small class="pull-right">{{ controller.file_path|format_file(controller.starting_line) }}</small></h3>
                        <pre><code class="php">{{ controller.source_code }}</code></pre>
                    {% else %}
                        <h3><a href="https://symfony.com/doc/current/controller.html">{{ 'title.controller_code'|trans }}</a></h3>
                        <pre><code>{{ 'not_available'|trans }}</code></pre>
                    {% endif %}

                    <h3><a href="https://symfony.com/doc/current/templates.html" target="_blank">{{ 'title.twig_template_code'|trans }}</a><small class="pull-right">{{ template.file_path|format_file(template.starting_line) }}</small></h3>
                    <pre><code class="twig">{{ template.source_code }}</code></pre>
                </div>
            </div>
        </div>
    </div>
</div>